It is proposed to purchase for use by a number of investigators equipment for the automated ion-exhange determination of amino acid compositions. Samples to be analyzed include acid hydrolyzates of proteins, peptides, and select phenylthiohydantoin amino acid derivatives produced during the course of automated protein sequencing operations. In addition to the principal and core investigators, members of the Divisions of Physical and Biological Sciences at the University of Chicago will have access to the instrumentation, as well as numerous researchers at other institutions who collaborate with our core investigators in protein structural studies. The equipment requested for the purpose, a Durrum Model D-502 analyzer, is the most accurate, sensitive, and time efficient instrument available today, and is, therefore, especially suited to the heavy demands of the proposed research. The analyzer will be located in the Cummings Life Science Center at The University of Chicago within an already existing protein structural analytical facility supervised by R.L. Heinrikson. He will direct the activities of a technician who will be responsible for the day to day operation and maintenance of the equipment and for communicating results to the appropriate investigator. Priorities for access to analyzer time will be established by the principal investigator, J.H. Law, in consultation with R.L. Heinrikson.